The capability to calculate the distribution of absorbed dose produced by photon beams and electron beams of the most general characteristics is of vital importance in radiotherapy. Conceptually, this model takes as a basis the empirical distributions along three mutually perpendicular reference lines in a "master field" and mathematical expressions to describe the effect of variation of field size, depth and focal distance. This concept is applied to the effects of beam-modifying devices as well. The approach is attractive from a theoretical as well as a practical point of view. The current investigations concern the generalization for irregular fields modified by irregular blocks, both for photon beams and electron beams.